This proposal is for a Research Scientist Award (RSA) that will enable me to conduct studies in the Developmental Psychobiology of human and infrahuman infants. The broad objective of the human research is to determine how classical conditioning contributes to forming the mother-infant bond in infants within the first hours following birth. The animal studies have four major objectives. The first concerns the role of infantile experience in determining adult mate selection. The second identifies the factors that underlie weaning. The third objective is to determine the contributions of the endogenous opioids to learning in suckling rats and to identify the biological circumstances under which such contributions are made. The final objective of the animal studies is to identify neurological substrates that are involved in the expression of certain affective behaviors and that mediate the classical conditioning of these behaviors to an odor. The RSA will allow me to devote the time required to fulfill these objectives and to read more widely in human development.